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Topics in Pokemon Biology: The History of Sinnoh's Battle Zone
Some centenarians alive today still remember the 3475 eruption of Mt. Stark, the fallout of which covered all of Sinnoh with a fine layer of ash, and caused a yearlong volcanic winter worldwide. The island northeast of Sinnoh, which had once been called Saharin, was covered with lava, which hardened into igneous rock. The eruption destroyed almost the entire ecosystem of the island, wiping the slate clean.
The Sinnoh government bought back the ruined land from the island's few surviving inhabitants, and for several decades the island remained in government control. But 40 years ago, the booming pokemon battle trade saw the founding of Battle Frontier™ Incorporated in Hoenn. This company saw promise in an empty landscape, and bought Saharin with the intent of turning it into a deluxe trainer's resort.
Naturally, the island would have been recolonized by flying and swimming pokemon from mainland Sinnoh, over thousands of years. But Battle Frontier™ Inc. was not satisfied with waiting. The company imported numerous pokemon species to the island and its surrounding waters, most not native to Sinnoh, for a greater tourist draw. The effort was justified by saying that little remained of the Saharin original fauna, although this was not entirely true. Several pokemon species survived by remaining underground during the eruption, including a tiny remnant of the island's endemic Heatran.
Regardless, the project was viewed as a wild success, and has earned Battle Frontier™ Inc billions. Saharin, now renamed 'The Battle Zone,' is now overrun with non-native pokemon, though some native species still hang on.